1. Field of the Invention
This invention relates to an ignition coil having a structure such that a transformer is housed in a case and, more particularly, to an ignition coil which requires connecting high-tension terminals and coil ends inside a case.
2. Description of the Related Art
FIGS. 5, 6, and 7 show a conventional ignition coil; FIG. 5 is a top view; FIG. 6 is a side view; and FIG. 7 is a vertical longitudinal sectional view. FIG. 6 shows a side of the ignition coil viewed from the left hand side of FIG. 7.
A coil unit 1 is accommodated in an accommodation portion 2b of a case 2. In a coil unit 1, a primary coil 1a and a secondary coil 1b are wound around a bobbin 1c, the primary coil 1a being wound inside the secondary coil 1b. The primary coil is a low-tension coil connected to a battery (not shown), and the secondary coil 1b is a high-tension coil connected to spark plugs (not shown).
The case 2 is formed by, for example, molding a plastic or the like. High-tension terminals 3a and 3b are external connection terminals of the secondary coil 1b and these terminals 3a and 3b are embedded in the case 2. The high-tension terminal 3a is a long terminal extending from the right side of the case 2 to the left end of the accommodation portion 2b as shown in the figures, and is connected to an extensional portion 4a of the secondary coil 1b, i.e., the left end of this coil by a solder 7 (FIG. 7). The high-tension terminal 3b is a short terminal extending from the right side of the case 2 to the right end of the accommodation portion 2b, and is also connected to an extensional portion 4b of the secondary coil 1b, i.e., the right end of this coil by the solder 7. The operation of connecting these high-tension terminals 3a and 3b and the extensional portions 4a and 4b by soldering is performed through an opening side 2a indicated by arrows B1 and B2 in FIG. 7. The high-tension terminals 3a and 3b respectively have at their right ends female connection portions 3a and 3d for connection on the outside of the case 2.
A core 5 has upper portions one of which extends into a cavity 1d of the coil unit 1 through another opening formed on the case 2, and the other of which extends into the cavity 1d through the opening side 2a. Lower portions of the core 5 are connected below the case 2. The core 5 can be separated into two parts and is formed by joining two parts together from both sides of the case 2 so that they are fitted in the coil unit 1 and the case 2, as shown in FIG. 7.
An epoxy resin 6 (FIG. 6) is injected into the accommodation portion 2b to fix the parts in the accommodation portion 2b while electrically insulating these parts. More specifically, the ignition coil is positioned so that the opening side 2a faces upward, and a thermosetting epoxy resin 6 is injected into the accommodation portion 2b in the direction of an arrow A of FIG. 5 so that the epoxy resin 6 enters gaps between the parts in the accommodation portion 2b, that is, the accommodation portion 2b is filled with the epoxy resin 6. Thereafter the epoxy resin 6 is set by being heated, and the parts accommodated in the accommodation portion 2b are thereby fixed and electrically isolated from each other. A pair of low-tension terminals 8 is provided as external connection terminals for the primary coil 1a and the terminals 8 are fixed in such a manner as to be exposed outside the case 2 through the opening side 2a when the epoxy resin 6 is injected. The pair of low-tension terminals 8 are connected to two ends of the primary coil 1a via, for example, lead wires 8a, but details of this connection are omitted in the figures and will not specifically be described. Although the epoxy resin is indicated by a reference numeral 6 in FIG. 6, each figure shows a state in which the epoxy resin is removed for ease of explanation of the internal structure of the ignition coil.
As mentioned above, for conventional ignition coils, the operation of soldering the high-tension terminals and the extensional portions which are the ends of the high-tension secondary coil is performed through one opening side of the case, as indicated by arrows B1 and B2 in FIG. 7. To connect the high-tension terminal and the extensional coil end portions on the side of the case remote from the opening side, it is necessary to increase the size of the case by considering the space for enabling soldering. Also, the size of the case is increased for another reason that since the high-tension terminals extend from one side of the coil, the height of the extensional portions of the secondary coil must be increased to prevent contact between the coil and the high-tension terminal extending over the coil.